Shelf Sea Biogeochemistry blog

Sunday, 23 November 2014

Measuring growth of the microbes

Ocean research cruise blog of Jonathan Sharples

Yesterday started with another of our pre-dawn set of measurements.
Fundamental biological measurements we need from these pre-dawn CTDs are
how fast the microbial plants (the phytoplankton) are absorbing and
using carbon and nutrients, and how fast the bacteria are growing by
using the organic matter available in the water. Think of these as the
two ends of a food chain, with the phytoplankton converting the
inorganic elements into organic material, and the bacteria breaking down
the organic material back into the inorganic. Between them we have the
zooplankton, and other marine animals, eating the organic material
provided by the phytoplankton, and in turn providing waste material that
the bacteria use.

Radioisotope lab1

Measuring uptake of elements by phytoplankton and bacteria requires
very careful laboratory work. The method involves using tiny quantities
of radioisotopes of the elements we are interested in (carbon, nitrogen,
phosphate, silicate) and incubating samples of seawater that have been
treated with these isotopes. After a set period of time the sample is
filtered to collect the phytoplankton or bacteria, and the activity of
the samples counted to tell us how much of the element the organisms
used. We have two laboratories dedicated to this work on the ship. Alex
Poulton (National Oceanography Centre, Southampton) and Kyle Mayers
(University of Southampton) are working in one to measure the
phytoplankton rates. Sharon McNeill from the Scottish Association for
Marine Science in Oban is dealing with the bacteria rates.
We steamed quickly over to the deep ocean side of the shelf edge
yesterday afternoon, and at about 8 pm we started the second of our line
of sample stations to measure iron in the seawater. This line started
in a deep canyon, and we are working up the wall of the canyon back
towards the continental shelf.